1. Field of Invention
The invention relates generally to display systems. More particularly, methods and apparatus for displaying complex characters on a monitor are disclosed.
2. Description of Relevant Art
Displaying the contents of WEB pages on standard television monitors has always been a challenging problem due in part to the fact that standard television monitors have a much lower resolution as compared to standard computer monitors. By way of example, FIG. 1 illustrates a conventional NTSC standard TV picture 100. The TV picture 100 is formed of an active picture area 102 that is the area of the TV picture 100 that carries picture information. Outside of the active picture area 102 is a blanking region 104 suitable for line and field blanking. The active picture area 102 uses frames 106, pixels 108 and scan lines 110 to form the actual TV image. The frame 106 represents a still image produced from any of a variety of sources such as an analog video camera, an analog television, etc. In systems where interlaced scan is used, each frame 106 represents a field of information. Frame 106 may also represent other breakdowns of a still image depending upon the type of scanning being used. Information in frame 106 is represented by any number of pixels 108. A pixel ( an acronym for "picture element") is the smallest distinguishable and resolvable area in an image as well as the discrete location of an individual photo-sensor in a solid state camera. Each pixel in turn represents digitized information and is often represented by 8 bits, although each pixel may be represented by any number of bits. Each scan line 110 includes any number of pixels 108, thereby representing a horizontal line of information within frame 106.
In NTSC video (a television standard using interlaced scan), for example, a field of information appears every 60th of a second, a frame (including 2 fields) appears every 30th of a second and the continuous presentation of frames of information produce a picture. An interlaced display is a display in which the lines are scanned alternately in two interwoven rasters. In a conventional interlaced display, there are several hundred horizontal lines in a frame (full screen). These lines are scanned from left to right, and from top to bottom. The refresh rate (number of frames scanned per second) varies, but it is normally between 60 and 100 Hz. Refresh rates slower than 60 Hz produce distracting screen flicker, which can cause headaches and eye fatigue. Since a computer monitor using progressive scan refreshes the frame of information on the screen every 30th of a second with no interlacing of frames, the problem of flicker is substantially eliminated in computer monitors using progressive scan techniques.
It is in part due to the combination of low resolution and the presence of image flicker that presents a substantial challenge to displaying WEB pages, digital images, text, and the like on standard NTSC format monitors. In order to display an image, such as an alphanumeric character on a television monitor, the character image is typically converted to what is referred to as a graphics bitmap suitable for storage in a memory device coupled to the television. Such memory devices are typically included in set top boxes used in conjunction with cable modems, WEBTV.TM. terminals, and the like.
A conventional approach to displaying the alphanumeric character includes preprocessing the character bitmap to reduce the flicker using various anti-aliasing techniques well known to those skilled in the art. Anti-aliasing is a technique used on a gray-scale or color bitmap displays to make diagonal edges appear smoother by setting pixels near the edge to intermediate colors according to where the edge crosses them. Typically, applying conventional anti-aliasing techniques to character bitmaps to reduce flicker has the effect of blurring the character image. In the case of simply connected characters such as, for example, those characters found in the Roman alphabet, this blurring presents no real problem since the characters remain substantially legible. However, for complex characters that are formed of many strokes, such as those found in the Chinese and Korean language, this blurring renders these multiply connected characters substantially illegible, or in some cases, changes the entire meaning of the character.
Therefore, what is desired are techniques for legibly displaying complex characters typical of, for example, the Chinese and Korean language, on a standard television monitor.